Mobile communication systems have been greatly advanced through 1st generation analog-type advanced mobile phone systems (AMPS) and 2nd generation cellular/personal communication service (PCS) systems. Recently, international mobile telecommunication-2000 (IMT-2000) systems have been developed and are widely used as 3rd generation high-rate data communication systems.
The 3GPP2 (3rd Generation Partnership Project2), which is a collaborative international standardization group, offers standards of a CDMA IMT-2000 system as IMT-2000 standards in order to provide multimedia mobile communication services. According to the above standards, a high rate packet data system called “1xEV (evolution)” based on an HDR (high data rate) proposed by Qualcom Incorporated, has been decided upon as an international standard high rate packet data system. A CDMA 2000 1xEV-DO (data optimized or data only) system has been upgraded from a CDMA 2000 1X system and is designed to transmit only data.
In the following description, the CDMA 2000 1X system is simply referred to as “1X system” and the CDMA 2000 1xEV-DO system is simply referred to as “1xEV-DO system” for the convenience of explanation.
The 1X system utilizes both circuit networks and packet networks and provides high-rate data services with a maximum transmission rate of 307.2 Kbps. In contrast, the 1xEV-DO system is dedicated for packet data and provides high-rate packet data services with a maximum transmission rate of 2.4 Mbps.
Currently, the 1xEV-DO system has been used together with the conventional 1X system. That is, both of the 1xEV-DO system and the conventional 1X system are installed in one wireless base station or a base station controller even though they are operated separately from each other. In other words, a transceiver of the wireless base station includes a channel card for the 1xEV-DO system and a channel card for the 1X system, respectively. In addition, the base station controller includes a data processing board for processing packet data transmitted from the 1xEV-DO system and a data processing board for processing data transmitted from the 1X system, respectively.
High-rate data are transmitted to a mobile communication terminal from a mobile communication system, such as the wireless base station or the base station controller, through the 1xEV-DO system. In addition, voice signals or low-rate data are transmitted to the communication terminal through the 1X system.
A hybrid access terminal capable of receiving communication services transmitted from the mobile communication system having both 1xEV-DO system and 1X system may periodically monitor each of the 1xEV-DO and 1X systems in a predetermined period of time. That is, the hybrid access terminal periodically and alternately searches the 1xEV-DO and 1X systems in an idle mode thereof and periodically searches the 1X system when the hybrid access terminal is in traffic with the 1xEV-DO system.
Particularly, the hybrid access terminal in traffic with the 1xEV-DO system periodically accesses to the 1X system and updates system resources, such as system messages and access messages, in order to respond to low-data call signals, such as voice call-accepted signals and short messages, which may be transmitted to the hybrid access terminal from the 1X system.
However, the hybrid access terminal must stay in the 1X system until the system resources have been completely updated whenever the hybrid access terminal periodically accesses to the 1X system even if the hybrid access terminal is in traffic with the 1xEV-DO system.
In addition, the 1xEV-DO system may perform a call drop operation if the 1xEV-DO system does not receive a signal from the hybrid access terminal within a predetermined period of time (for example, 5.12 seconds) when the hybrid access terminal is in traffic with the 1xEV-DO system. That is, regardless of reasons thereof, if the 1xEV-DO system searches no signal from the hybrid access terminal within the predetermined period of time, the 1xEV-DO system performs the call drop operation with respect to the hybrid access terminal in order to efficiently utilize the system resources.
However, the call drop may lower reliability of communication services and cause inconvenience and troubles to users, who do not want the call drop with respect to the 1x EV-DO system.